Electrically operated valves are constructed such that a valve element is opened and closed by a motor driving force. Their major features include that a large valve element driving force is acquired and that the open and close operations can be performed by remote control. Because of these features, electrically operated valves are used widely, for example, in a large plant where large diameter piping is equipped or in the piping of a nuclear power station where operation by hand is restricted. Their major application is a valve for full open/full close of a passage in piping rather than a valve for flow rate adjustment.
Such an electrically operated valve comprises: a valve element for opening and closing a passage in piping; a valve element driving section for performing the open and close operation of the valve element in response to a revolving force of a worm revolved by a motor; and a spring cartridge into which a dish spring expanded and contracted in response to a thrust generated in the worm in the valve element driving section is installed in a state of being compressed by a prescribed compression force (this compression force is referred to as a “compressed load”). Then, the driving force obtained from the compression state of the spring cartridge, that is, a torque of the electrically operated valve, is imparted to the valve element driving section, so that the open and close operation of the valve element is performed. Then, when the compression amount of the spring cartridge reaches a restriction value, the motor is stopped. By virtue of this, an appropriate open and close holding force is achieved in the valve so that a valve function of high reliability is ensured, while an excessive driving force is avoided so that damage is prevented.
On the other hand, in the electrically operated valve, in order that its function should be maintained over a long term, soundness need be checked in the function of the electrically operated valve itself. In addition, soundness need be checked in the valve element driving section and the like (including the electric part) for transmitting the revolving force of the worm to the valve element side. The points of interest in this diagnosis include whether the valve element is driven with an appropriate torque, whether an appropriate holding torque is ensured in the full open and full close states of the valve element, whether setting is appropriate in the torque switch for stopping the motor automatically when a necessary torque has been imparted, and to what extent wear has progressed in the valve element driving section and the like. Among these diagnosis items, the diagnosis on the torque [which is a physical quantity having a fixed relation with the compression force of the spring cartridge, that is, a torque obtained from the compression force of the spring cartridge; the value is acquired in accordance with (torque)=(spring cartridge compression force)×r (where r denotes ½ of the pitch circle diameter of the worm wheel; see FIGS. 1 and 2] is expected to be most important because of the past examples where a large number of troubles are attributed to inappropriateness of the torque. Thus, in the prior art, various kinds of electrically operated valve diagnosing methods have been proposed concerning the torque.
For example, as described in Patent Document 1, a strain gauge is stuck on a part of a spring cartridge, so that the compression force of the spring cartridge, that is, the value of a torque corresponding to this, is acquired by the strain gauge in an operating state of the electrically operated valve. Then, on the basis of this acquired torque, diagnosis is performed on the torque. This approach is a so-called “built-in torque sensor method”.
Further, a technique has been proposed in which in the diagnosis work, detecting means for the torque is attached to the outer end side of the spring cartridge so that on the basis of the acquired torque, the electrically operated valve is diagnosed concerning the torque (see Patent Documents 2 and 3).
The approach disclosed in Patent Document 2 is a so-called “externally attached torque sensor method”. In this method, compression force detecting means for detecting the compression force acting on the spring cartridge and movement amount detecting means for detecting the compression amount of the spring cartridge, that is, the movement amount of the worm are attached to the outer end side of the spring cartridge. Then, in a state that the electrically operated valve is operated, correlation is acquired between the compression amount of the spring cartridge and the compression force corresponding to this which have been detected by these compression force detecting means and movement amount detecting means. After that, the compression amount is measured so that the actually acting compression force is acquired from this measured value with reference to the correlation. Further, on the basis of this compression force, the torque actually acting from the worm to the valve element driving section is acquired. Then, on the basis of this torque, diagnosis is performed on the torque of the electrically operated valve.
In this method, because of the structure of the compression force detecting means, the compression force can be detected only at any one of open operation and close operation of the electrically operated valve. However, regardless of whether the operation direction of the electrically operated valve is in the open operation direction or the close operation direction, the same situation occurs and no difference arises in the point that the spring cartridge is compressed. Thus, when the compression amount of the spring cartridge is merely measured at both of open operation and close operation, the compression force on the other side is also obtained. That is, in a case that the compression amount and the value obtained by converting this compression amount into the torque are acquired as data, when the compression amount is measured, the corresponding torque is obtained at each of open operation and close operation of the electrically operated valve.
On the other hand, what is disclosed in Patent Document 3 is a so-called “spring compression method”. In this method, a strain gauge, position detecting means, and compressing means are attached on the outer end side of the spring cartridge (i.e., an end of the spring cartridge opposite to the worm). Then, in a state that the operation of the electrically operated valve is stopped, the dish spring of the spring cartridge is compressed from the outside by the compressing means. In this state, the compression force on the spring cartridge is acquired by the strain gauge, while the compression amount of the spring cartridge is acquired by the position detecting means, so that relation is acquired between the compression amount of the spring cartridge and the compression force corresponding to this. Next, in a state that the electrically operated valve is operated, the compression amount is measured so that the actually acting compression force is acquired from this measured value. Further, on the basis of this compression force, the torque actually acting from the worm to the valve element driving section is acquired. Then, on the basis of this torque, diagnosis is performed on the torque of the electrically operated valve.
(Patent Document 1)
International Laid-Open Patent Application No. WO95/14186 (line 19 in lower right column at page 3 through line 29 in upper right column at page 4, and FIGS. 2 and 3)
(Patent Document 2)
Japanese Patent Publication No. 2982090 (Paragraphs [0021]-[0031] and FIGS. 1-4)
(Patent Document 3)
Japanese Laid-Open Patent Application No. H7-310845 (Paragraphs [0028]-[0036] and FIG. 2)